1. Field of the Invention
This invention relates to the field of infrared detection, and more particularly to a thermal damper for minimizing temperature variation in an infrared detector.
2. Description of Related Art
Infrared detectors are often used in conjunction with missiles and night vision systems to sense the presence of electromagnetic radiation having wavelengths of 1-15 .mu.m. Because they are often most sensitive when operating at low temperatures, detectors such as those fabricated from mercury-cadmium-telluride generally require a cryoengine assembly to produce and maintain the necessary low operating temperature. Such cryoengine assemblies are typically used in conjunction with an evacuated dewar in which an infrared detector is placed. The dewar is evacuated to remove gases which would otherwise occupy the region surrounding the detector so that heat loss through convection and conduction is minimized.
The detector is typically cooled by placing an indented region ("coldwell") of the dewar in contact with an expansion chamber ("coldfinger") of the cyroengine assembly. Alternatively, the coldfinger of the cyroengine assembly is used as the coldwell of the dewar to enable the detector to be mounted on the cryoengine coldfinger. The cryoengine assembly produces cooling by sequential compression of the working fluid such as helium, removal of the heat of compression of the fluid, and subsequent expansion of the working fluid in the coldfinger. Because the detector is in thermal communication with the coldfinger, the expansion of the working fluid causes heat to be withdrawn from the detector.
Although the necessary operating temperatures can be achieved by the devices generally described above, the cyclical nature of the expansion of the working fluid would often produce a cyclical variation in the detector operating temperature. Because infrared detectors are often temperature sensitive, this cyclical variation in operating temperature would produce a corresponding variation in the output signal of the detector. Thermal masses or resistances located between the detector and the coldfinger were often employed to minimize this temperature variation. While such solutions were somewhat effective in reducing temperature variation, they would often increase the time required to initially cool the detector from ambient to the necessary operating temperature. In addition, the use of a thermal resistor would often hinder the flow of thermal energy between the coldfinger and the detector, which would in turn generally require the use of a cryoengine assembly having a greater cooling capacity than would otherwise be necessary.